Low rf noise axial compensation connector



March 1l, 1969 Q N SEWELL 3,432,779

LOW RF NOISE AXIAL COMPENSATION CONNECTOR Filed March 9, 1967 l l 1 1 l l ,1

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United States Patent O 3,432,779 LOW RF NOISE AXIAL COMPENSATION CONNECTOR Donald Nelson Sewell, Acton, Mass., assigner to Dielec tric Products Engineering Company, Inc., Littleton, Mass., a corporation of Michigan Filed Mar. 9, 1967, Ser. No. 621,976 U.S. Cl. 333-97 11 Claims Int. Cl. H01p 1/06 ABSTRACT oF THE DISCLOSURE A simple, economical low RF noise axial compensation joint for a coaxial transmission line employing tubular inner and outer conductors. The end of one inner conductor section is reduced in a series of two steps, a frst step on which a layer of polytetrafluoroethylene is disposed and over which the end of the other conductor section is received in clearance relation, and a second step of larger dimensional magnitude than the first step on which a Phosphor bronze spring formed in a loop is disposed. The spring provides the sole electric circuit connection between the two inner conductor sections and rolls along the surfaces when the sections are moved axially relative to one another.

Summary of invention This invention relates to electrical connector arrangements and more particularly to electrical connector arrangements of particular advantage in coupling together adjacent inner conductor segments of a coaxial transmission line.

In a coaxial transmission line axial movement of the outer and inner conductors may be of different magnitudes, for example, under thermal stress. Structure for compensating this relative movement of the inner and outer conductors are required. In such electrical transmission compensating structures it is important to minimize the IRF noise introduced due to such differential movement; and also to minimize the degradation of the conductors and/or introduction of contaminants, such as particles of conductor material which might be produced by a sliding joint, for example. =Either condition would adversely affect the electrical signal transmission characteristics of the transmission line.

An object of the invention is to provide a novel and improved electrical connector structure particularly adapted for use in coaxial electrical transmission lines which provides compensation for axial movement of the line segments coupled by the connector structure.

Another object of the invention is to provide a novel and improved low RF noise compensation joint structure for use in an RF electrical transmission line which joins two conductor segments and permits limited axial movement between the segments and which has a VSWR characteristic of less than 1.02 over a frequency range of up to 1 gHz.

Still another object of the invention is to provide a novel and improved axial movement compensation structure for use in coaxial RF transmission lines that is economical to manufacture and reliable in operation.

The invention features an electrical conductor compensation joint connecting two conductor sections together in electrically conductively end-to-end relation in a substantially axial direction and allowing relative movement in that axial direction. One end of one of the sections has a predetermined cross section of tubular configuration and the other section has the same outer cross sectional configuration except at its end adjacent the one section which end is of similar but smaller cross sectional 3,432,779 Patented Mar. 11, 196

configuration so that it fits inside the first end in overlapping relation. A loop of resilient electrically conductive material of circular cross section is disposed between the overlapping surfaces for rolling movement therealong, the

loop lying in a plane perpendicular to the axial direction of the conductor sections and the conductive material providing the sole electric circuit connection between the adjacent electrical conductor sections.

In a particular embodiment of the invention, both conductor sections are tubular and the end of the other section is reduced in a series of two steps, a first step on which a thin layer of electrical insulation is disposed and which receives the end of the one section is clearance relation, and a second step of larger dimensional magnitude on which the electrically conductive loop is disposed.

The loop in this embodiment is a helix of resilient wire which provides a multiplicity of contact points between the overlapping surfaces of the two conductor sections. The layer of electrical insulation provides an additional safeguard to restrict the current .flow to the path including the conductive loop. This structure provides a simple economical low noise axial compensation joint in which distortion of the electric field between the inner and outer conductors due to the presence of the joint is minimized.

Of FIG. 4;

FIG. 3 is a cross-sectional view taken along line 3--3 of FIG. 4;

FIG. 4 is a longitudinal sectional view of the joint between the inner conductor sections in a first axial position; and

FIG. 5 is a view of the joint taken along line 5 5 of FIG. 4, showing a second axial position of the adjacent inner conductor sections.

Description of particular embodiment There is shown in FIG. l a coaxial transmission line having a tubular outer conductor section 10 and a series of tubular inner conductor sections 12, 14, 16, disposed within section 10. Suitable coaxial support structures such as disc member 18 of dielectric material supports three inner conductor sections in coaxial relation with outer conductor 10.

Each tubular inner conductor section is copper tubing of 0.025 inch wall thickness and has formed at one end a stepped series of two annular surfaces 20, 22, the diameter of surface 20 being about `0.060 inch less than the outer diameter of the section and the diameter of surface 22 being about 0.200 inch less than the diameter of surface 20. Disposed on surface 20 is a plastic sleeve 24 of polytetrafluoroethylene 0.003 inch in thickness. This .'sleeve may be mechanically (e.g. adhesively) secured over surface 20 with a lip 2-6 at one end.

A loop 30 of resilient electrically conductive material of circular cross section, which in this embodiment is a 5 helical coil (0.125 inch O.D.) of 0.008 inch Phosphor bronze wire wound at a pitch of about four times the wire diameter, is disposed between surface 22 and surface 32 (the inner surface of the conductor section that overlies the series of stepped surfaces). The length of surface 20 is 0.45 inch and the length of surface 20 is somewhat longer.

A suitable latch structure secures the adjacent inner :onductor sections together -While permitting a degree of `reedom of relative axial movement. The illustrated latch :tructure includes a retaining clip 34 secured to section L4 (as indicated in FIG. 2) by rivets 36 that are disposed ,n depressions 38 so that the rivets do not protrude bevond the nominal O.D. of tube 14. Clip 34 has an aper- :ure 40 that receives end portions 42 of cooperating spring clip 44 which is secured on rod 46 by rivet 48. Each end of rod 46 is recessed and receives a plunger element S0 which is biased outwardly by spring 52 disposed in the recessed end of rod 46. The tips of the plunger elements protrude through recessed apertures 54 in cooperating conductor section 16 as indicated in FIGS. 4 and 5 to secure the spring clip structure 44 in place on section 16 while not protruding beyond the nominal O.D. of tube 16.

In assembling the connector, spring 30 is positioned on surface 22 and then the end of section 16 is slid over spring 30, distorting it to the position indicated in FIG. 2. Spring 30 rolls along surface 22 under the influence of surface 32 until it contacts the transition between surfaces and 22. It is lheld in that position while surface 32 continues to be moved over surface 20 toward lip 26 and after latch ends 42 of spring clip 44 pass through aperture 40 in cooperating retaining clip 34 until the end of section 16 abuts lip 26 (the position shown in FIG. 5).

In this position the sections 14, 16 are latched together while they are permitted to move relative to one another in the axial direction. The latch structure elements 34, 44 limit the extent of axial movement, which in this embodiment is about 0.40 inch. The dimensions of sleeve 24 on surface 20 is correlated `with the dimensions of surface 22 and conductor loop 30 to provide mechanical support which protects the conductor loop 30 from excessive side loading. The joint may be disassembled merely by depressing plunger elements 50 to release them from apertures 54.

In the assembled transmission line, the main path of electric current flow along the inner conductor from one section to the next is from conductor 14 through conductive loop spring 30 to section 16. Sleeve 24 acts to restrict this current flow to that path. The resilient spring 30, of circular cross section, rolls between surfaces 22 and 32 as the conductor sections 14, 16 move axially between the positions shown in FIGS. 4 and 5. This structure thus permits axial movement between sections 14, 16 while maintaining electrical continuity through a multiplicity of points without any slipping so there is no tendency to scrape particles of metal loose from the contact surfaces which scraping degrades the contact surfaces and produces conductive contaminants which tend to irnpair the integrity of the insulator structures. This rolling contact construction provides an electrically conductive joint for RF electrical energy having uniform characteristics over the permitted range of axial movement and a VSWR of less than 1.02 over a frequency range up to 1 gHz. while minimizing the possibility of a differential voltage being produced at the joint contact area which would result in a series arcing condition. Such series arcing produces electrical noise which degrades the electrical performance of the system and erodes the contact surfaces so that increased heating results which accelerates the degradation of the contact structure and the efficiency and quality of RF energy transmission. The insulating sleeve further protects the conductor surfaces, restricts the path of electric current fiow to the rolling loop, and controls the magnitude of side loading on the loop without any significant impeding of the relative axial movement of the inner conductor sections under thermal or other stress. Thus the invention provides a simple yet efficient and reliable RF compensation joint capable of economical manufacture and easy assembly.

While a particular embodiment of the invention has been shown and described, modifications thereof will be apparent to those skilled in the art and therefore it is not intended that the invention be limited to the disclosed embodiment nor to details thereof and departures may be made therefrom within the spirit and scope of the invention as defined in the claims.

What is claimed is:

1. A low loss RF electrical connector compensation structure for connecting together two electrical conductor sections while permitting movement, in a substantially axial direction, of said conductor sections relative to each other, comprising:

a first conductor section of predetermined tubular cross sectional configuration,

a second conductor section having a major portion of the same outer cross sectional configuration and a cooperating end portion of similar but smaller cross sectional configuration,

said end portion being disposed within the end of said first conductor in overlapping relation,

and a loop of resilient electrically conductive material of circular cross section,

said loop lying in a plane perpendicular to said axial direction and being disposed between said overlapping portions of said conductor sections in rolling contact with said overlapping portions,

said conductive material providing the sole electric circuit connection between said adjacent electrical conductor sections and said compensation structure having a VSWR characteristic of less than 1.02 over a frequency range up to l gHz.

2. The compensation structure as claimed in claim 1 wherein said loop is a helical spring.

3. The compensation structure as claimed in claim 1 wherein said cooperating end portion has formed thereon a series of two surfaces of similar cross sectional configuration, a first surface adapted to receive the end of said first conductive section in overlapping, clearance relation, and a second surface on which said conductive loop is disposed.

4. The compensation structure as claimed in claim 3 and further including a layer of electrical insulation diS- posed on said first surface of dimension so that the end of said first conductor section overlies said insulation in clearance relation.

5. The compensation structure as claimed in claim 1 and further including a latch structure for mechanically connecting said first and second conductor sections together while permitting limited axial movements of said conductor sections relative to each other.

6. For use in a coaxial electrical transmission line comprising:

a tubular outer conductor and structure for supporting an inner conductor in coaxial relation to said outer conductor,

a tubular inner conductor structure comprising two axially disposed sections of the same outer configuration over substantially their entire lengths joined together in an end-to-end relation,

a first inner conductor section having an end of reduced diameter providing an annular surface of significant axial length,

the second inner conductor section having an annular end overlying said reduced diameter annular surface,

and a loop of resilient electrically conductive material of circular cross section,

said loop lying in a plane perpendicular to said axial direction and being disposed between said overlapping conductor section ends in rolling contact with said conductor section ends,

said conductive material providing the sole electric circuit connection between said adjacent electrical conductor sections, and having a VSWR characteristic of less than 1.02 over a frequency range up to 1 gHz.

7. The structure as claimed in claim 6 wherein the annular resilient electrically conductive member of circular cross section is a helical spring.

8. The structure as claimed in claim 6 and further including a latch mechanically connecting said adjacent inner conductor sections together 'while permitting limited axial movement of said adjacent sections relative to each other.

9. The structure as claimed in claim 8 wherein said latch structure includes a resilient latch element secured to one conductor section and cooperating in latching engagement with a second latch element secured to the other conductor section, one of said latch elements being resiliently secured to its conductor section.

10. The structure as claimed in claim 9 wherein said reduced diameter annular surface has formed thereon a series of two surfaces of similar cross sectional configuration, a first surface adapted to receive the end of said tirst conductive section in overlapping, 'clearance relation, and

a second surface on which said conductive loop disposed.

11. The structure as claimed in claim 10 and furthe including a layer of electrical insulation disposed on sai first surface of dimension so that the end of said iin conductor section overlies said insulation in clearanc relation.

References Cited UNITED STATES PATENTS 3,319,214 5/1967 Sewell 339-17 ELI LIEBERMAN, Primary Examiner.

L. ALLAHUT, Assistant Examiner.

U.S. C1. XR. 339-9. 177 

